1. Field of the Invention
The invention is directed to an improved fuel injection valves of the type that have two valve needles guided one inside the other.
2. Description of the Prior Art
Fuel injection valves of the type which this invention is concerned are known, for example, from German Patent Disclosure 41 15 477 A1. At their ends oriented toward the combustion chamber, the two valve needles each control at least one injection opening and can be triggered so that either only the outer valve needle opens part of the injection openings, or both valve needles open, thus opening all of the injection openings. This allows the injection cross-section to be optimally adjusted as a function of the load of the internal combustion engine. The longitudinal movement of the valve needles in the bore is governed by the relationship between an opening force acting on the valve needles and a counterpoised closing force. The opening force is generated by the hydraulic pressure on corresponding pressure surfaces of the valve needles, while the closing force in the known fuel injection valves is generated either by springs or by hydraulic forces. The known fuel injection valve has the disadvantage the it is not possible to freely control the opening time and opening duration of the two needles. The outer valve needle opens in a pressure-controlled manner in opposition to the force of a closing spring, while the inner valve needle—in addition to the closing force of a closing spring—is subjected to a force generated by the hydraulic pressure in a control chamber. A solenoid valve, however, can only control whether or not the inner valve needle opens during an injection cycle. The solenoid valve cannot influence the opening behavior of the outer valve needle. This limits the control of the exact onset of injection and the precise injection quantity, which naturally also makes it harder to further optimize combustion.